administration has repeatedly pressed congress to increase spending on bridges and roads. in march, the president visited the port of miami. >> we still got too many roads that are in disrepair, too many bridges that aren't safe. we don't have to accept that for america. we can do better. we can build better. >> ifill: but republicans, led by house speaker john boehner, have resisted spending more unless it's paid for. >> it's easy to go out there and be santa claus and talk about all these things you want to give away, but, at some point, somebody's got to pay the bill. >> ifill: federal officia estimate it would take about $20 billion a year to address all of the nation's bridge problems over each of 15 years. that's about $8 billion more than federal, state and local governments spend now. we take up some of the questions raised by all this now with two people who watch this field. casey dinges is the senior managing director of the american society of civil engineers. and dan mcnichol is an author and infrastructure analyst. he's spent the past year writing the history